diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..530c14c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*~
+/.idea
+/target
diff --git a/.mvn/jvm.config b/.mvn/jvm.config
new file mode 100644
index 0000000..5b7360a
--- /dev/null
+++ b/.mvn/jvm.config
@@ -0,0 +1 @@
+--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
diff --git a/.mvn/maven.config b/.mvn/maven.config
new file mode 100644
index 0000000..f8d5e4d
--- /dev/null
+++ b/.mvn/maven.config
@@ -0,0 +1 @@
+-Drevision=0.1.0-SNAPSHOT
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..0a04128
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
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+License, supplemented by the additional permissions listed below.
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diff --git a/COPYING.GPL b/COPYING.GPL
new file mode 100644
index 0000000..f288702
--- /dev/null
+++ b/COPYING.GPL
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+copyright holder, and you cure the violation prior to 30 days after
+your receipt of the notice.
+
+  Termination of your rights under this section does not terminate the
+licenses of parties who have received copies or rights from you under
+this License.  If your rights have been terminated and not permanently
+reinstated, you do not qualify to receive new licenses for the same
+material under section 10.
+
+  9. Acceptance Not Required for Having Copies.
+
+  You are not required to accept this License in order to receive or
+run a copy of the Program.  Ancillary propagation of a covered work
+occurring solely as a consequence of using peer-to-peer transmission
+to receive a copy likewise does not require acceptance.  However,
+nothing other than this License grants you permission to propagate or
+modify any covered work.  These actions infringe copyright if you do
+not accept this License.  Therefore, by modifying or propagating a
+covered work, you indicate your acceptance of this License to do so.
+
+  10. Automatic Licensing of Downstream Recipients.
+
+  Each time you convey a covered work, the recipient automatically
+receives a license from the original licensors, to run, modify and
+propagate that work, subject to this License.  You are not responsible
+for enforcing compliance by third parties with this License.
+
+  An "entity transaction" is a transaction transferring control of an
+organization, or substantially all assets of one, or subdividing an
+organization, or merging organizations.  If propagation of a covered
+work results from an entity transaction, each party to that
+transaction who receives a copy of the work also receives whatever
+licenses to the work the party's predecessor in interest had or could
+give under the previous paragraph, plus a right to possession of the
+Corresponding Source of the work from the predecessor in interest, if
+the predecessor has it or can get it with reasonable efforts.
+
+  You may not impose any further restrictions on the exercise of the
+rights granted or affirmed under this License.  For example, you may
+not impose a license fee, royalty, or other charge for exercise of
+rights granted under this License, and you may not initiate litigation
+(including a cross-claim or counterclaim in a lawsuit) alleging that
+any patent claim is infringed by making, using, selling, offering for
+sale, or importing the Program or any portion of it.
+
+  11. Patents.
+
+  A "contributor" is a copyright holder who authorizes use under this
+License of the Program or a work on which the Program is based.  The
+work thus licensed is called the contributor's "contributor version".
+
+  A contributor's "essential patent claims" are all patent claims
+owned or controlled by the contributor, whether already acquired or
+hereafter acquired, that would be infringed by some manner, permitted
+by this License, of making, using, or selling its contributor version,
+but do not include claims that would be infringed only as a
+consequence of further modification of the contributor version.  For
+purposes of this definition, "control" includes the right to grant
+patent sublicenses in a manner consistent with the requirements of
+this License.
+
+  Each contributor grants you a non-exclusive, worldwide, royalty-free
+patent license under the contributor's essential patent claims, to
+make, use, sell, offer for sale, import and otherwise run, modify and
+propagate the contents of its contributor version.
+
+  In the following three paragraphs, a "patent license" is any express
+agreement or commitment, however denominated, not to enforce a patent
+(such as an express permission to practice a patent or covenant not to
+sue for patent infringement).  To "grant" such a patent license to a
+party means to make such an agreement or commitment not to enforce a
+patent against the party.
+
+  If you convey a covered work, knowingly relying on a patent license,
+and the Corresponding Source of the work is not available for anyone
+to copy, free of charge and under the terms of this License, through a
+publicly available network server or other readily accessible means,
+then you must either (1) cause the Corresponding Source to be so
+available, or (2) arrange to deprive yourself of the benefit of the
+patent license for this particular work, or (3) arrange, in a manner
+consistent with the requirements of this License, to extend the patent
+license to downstream recipients.  "Knowingly relying" means you have
+actual knowledge that, but for the patent license, your conveying the
+covered work in a country, or your recipient's use of the covered work
+in a country, would infringe one or more identifiable patents in that
+country that you have reason to believe are valid.
+
+  If, pursuant to or in connection with a single transaction or
+arrangement, you convey, or propagate by procuring conveyance of, a
+covered work, and grant a patent license to some of the parties
+receiving the covered work authorizing them to use, propagate, modify
+or convey a specific copy of the covered work, then the patent license
+you grant is automatically extended to all recipients of the covered
+work and works based on it.
+
+  A patent license is "discriminatory" if it does not include within
+the scope of its coverage, prohibits the exercise of, or is
+conditioned on the non-exercise of one or more of the rights that are
+specifically granted under this License.  You may not convey a covered
+work if you are a party to an arrangement with a third party that is
+in the business of distributing software, under which you make payment
+to the third party based on the extent of your activity of conveying
+the work, and under which the third party grants, to any of the
+parties who would receive the covered work from you, a discriminatory
+patent license (a) in connection with copies of the covered work
+conveyed by you (or copies made from those copies), or (b) primarily
+for and in connection with specific products or compilations that
+contain the covered work, unless you entered into that arrangement,
+or that patent license was granted, prior to 28 March 2007.
+
+  Nothing in this License shall be construed as excluding or limiting
+any implied license or other defenses to infringement that may
+otherwise be available to you under applicable patent law.
+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/pom.xml b/pom.xml
new file mode 100644
index 0000000..874369e
--- /dev/null
+++ b/pom.xml
@@ -0,0 +1,262 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"
+  xmlns="http://maven.apache.org/POM/4.0.0"
+  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>eu.mulk.jgvariant</groupId>
+  <version>0.1.0-SNAPSHOT</version>
+
+  <artifactId>jgvariant-core</artifactId>
+  <packaging>jar</packaging>
+
+  <name>JGVariant</name>
+  <url>https://gerrit.benkard.de/plugins/gitiles/jgvariant</url>
+
+  <description>
+    GVariant serialization and deserialization.
+  </description>
+
+  <licenses>
+    <license>
+      <name>GNU Lesser General Public License v3.0 or later</name>
+      <url>https://www.gnu.org/licenses/lgpl-3.0.html</url>
+    </license>
+  </licenses>
+
+  <developers>
+    <developer>
+      <name>Matthias Benkard</name>
+      <email>code@mulk.eu</email>
+      <organization>Matthias Benkard</organization>
+      <organizationUrl>https://matthias.benkard.de</organizationUrl>
+    </developer>
+  </developers>
+
+  <scm>
+    <connection>scm:git:https://gerrit.benkard.de/jgvariant</connection>
+    <developerConnection>scm:git:ssh://gerrit.benkard.de:29418/jgvariant</developerConnection>
+    <url>https://gerrit.benkard.de/plugins/gitiles/jgvariant</url>
+  </scm>
+
+  <properties>
+    <maven.compiler.parameters>true</maven.compiler.parameters>
+    <maven.compiler.release>17</maven.compiler.release>
+
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
+
+    <compiler-plugin.version>3.8.1</compiler-plugin.version>
+    <failsafe-plugin.version>${surefire-plugin.version}</failsafe-plugin.version>
+    <jar-plugin.version>3.2.0</jar-plugin.version>
+    <maven-gpg-plugin.version>1.5</maven-gpg-plugin.version>
+    <maven-javadoc-plugin.version>3.2.0</maven-javadoc-plugin.version>
+    <maven-source-plugin.version>2.2.1</maven-source-plugin.version>
+    <nexus-staging-plugin.version>1.6.8</nexus-staging-plugin.version>
+    <spotless-plugin.version>2.17.6</spotless-plugin.version>
+    <surefire-plugin.version>3.0.0-M5</surefire-plugin.version>
+
+    <errorprone.version>2.10.0</errorprone.version>
+    <google-java-format.version>1.13.0</google-java-format.version>
+    <jetbrains-annotations.version>20.1.0</jetbrains-annotations.version>
+    <junit-jupiter.version>5.8.1</junit-jupiter.version>
+  </properties>
+
+  <distributionManagement>
+    <snapshotRepository>
+      <id>ossrh</id>
+      <url>https://s01.oss.sonatype.org/content/repositories/snapshots</url>
+    </snapshotRepository>
+  </distributionManagement>
+
+  <dependencyManagement>
+    <dependencies>
+      <dependency>
+        <groupId>com.google.errorprone</groupId>
+        <artifactId>error_prone_annotations</artifactId>
+        <version>${errorprone.version}</version>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+
+  <dependencies>
+    <!-- Annotations -->
+    <dependency>
+      <groupId>com.google.errorprone</groupId>
+      <artifactId>error_prone_annotations</artifactId>
+      <optional>true</optional>
+    </dependency>
+    <dependency>
+      <groupId>org.jetbrains</groupId>
+      <artifactId>annotations</artifactId>
+      <version>${jetbrains-annotations.version}</version>
+      <optional>true</optional>
+    </dependency>
+
+    <!-- Testing -->
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <version>${junit-jupiter.version}</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <version>${junit-jupiter.version}</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+  <build>
+
+    <pluginManagement>
+
+      <plugins>
+
+        <plugin>
+          <artifactId>maven-surefire-plugin</artifactId>
+          <version>${surefire-plugin.version}</version>
+        </plugin>
+
+        <plugin>
+          <artifactId>maven-failsafe-plugin</artifactId>
+          <version>${failsafe-plugin.version}</version>
+        </plugin>
+
+        <plugin>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <version>${compiler-plugin.version}</version>
+          <configuration>
+            <fork>true</fork>
+            <compilerArgs>
+              <arg>-XDcompilePolicy=simple</arg>
+              <arg>-Xplugin:ErrorProne</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED</arg>
+              <arg>-J--add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED</arg>
+              <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED</arg>
+              <arg>-J--add-opens=jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED</arg>
+            </compilerArgs>
+            <annotationProcessorPaths>
+              <path>
+                <groupId>com.google.errorprone</groupId>
+                <artifactId>error_prone_core</artifactId>
+                <version>${errorprone.version}</version>
+              </path>
+            </annotationProcessorPaths>
+          </configuration>
+        </plugin>
+
+        <plugin>
+          <artifactId>maven-jar-plugin</artifactId>
+          <version>${jar-plugin.version}</version>
+        </plugin>
+
+      </plugins>
+
+    </pluginManagement>
+
+    <plugins>
+
+      <plugin>
+        <groupId>com.diffplug.spotless</groupId>
+        <artifactId>spotless-maven-plugin</artifactId>
+        <version>${spotless-plugin.version}</version>
+        <configuration>
+          <java>
+            <removeUnusedImports/>
+            <importOrder>
+              <order>java,javax,org,com,de,io,dagger,eu.mulk,</order>
+            </importOrder>
+            <googleJavaFormat>
+              <version>${google-java-format.version}</version>
+              <style>GOOGLE</style>
+            </googleJavaFormat>
+          </java>
+        </configuration>
+      </plugin>
+
+      <plugin>
+        <groupId>org.sonatype.plugins</groupId>
+        <artifactId>nexus-staging-maven-plugin</artifactId>
+        <version>${nexus-staging-plugin.version}</version>
+        <extensions>true</extensions>
+        <configuration>
+          <serverId>ossrh</serverId>
+          <nexusUrl>https://s01.oss.sonatype.org/</nexusUrl>
+          <autoReleaseAfterClose>true</autoReleaseAfterClose>
+        </configuration>
+      </plugin>
+
+    </plugins>
+  </build>
+
+  <profiles>
+
+    <profile>
+      <id>release</id>
+
+      <build>
+        <plugins>
+
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-source-plugin</artifactId>
+            <version>${maven-source-plugin.version}</version>
+            <executions>
+              <execution>
+                <id>attach-sources</id>
+                <goals>
+                  <goal>jar-no-fork</goal>
+                </goals>
+              </execution>
+            </executions>
+          </plugin>
+
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-javadoc-plugin</artifactId>
+            <version>${maven-javadoc-plugin.version}</version>
+            <executions>
+              <execution>
+                <id>attach-javadocs</id>
+                <goals>
+                  <goal>jar</goal>
+                </goals>
+              </execution>
+            </executions>
+          </plugin>
+
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-gpg-plugin</artifactId>
+            <version>${maven-gpg-plugin.version}</version>
+            <configuration>
+              <keyname>code@mulk.eu</keyname>
+            </configuration>
+            <executions>
+              <execution>
+                <id>sign-artifacts</id>
+                <phase>verify</phase>
+                <goals>
+                  <goal>sign</goal>
+                </goals>
+              </execution>
+            </executions>
+          </plugin>
+
+        </plugins>
+      </build>
+    </profile>
+
+  </profiles>
+
+</project>
diff --git a/src/main/java/eu/mulk/jgvariant/core/Decoder.java b/src/main/java/eu/mulk/jgvariant/core/Decoder.java
new file mode 100644
index 0000000..2ebd0af
--- /dev/null
+++ b/src/main/java/eu/mulk/jgvariant/core/Decoder.java
@@ -0,0 +1,418 @@
+package eu.mulk.jgvariant.core;
+
+import static java.nio.ByteOrder.LITTLE_ENDIAN;
+
+import eu.mulk.jgvariant.core.Value.Array;
+import eu.mulk.jgvariant.core.Value.Bool;
+import eu.mulk.jgvariant.core.Value.Float64;
+import eu.mulk.jgvariant.core.Value.Int16;
+import eu.mulk.jgvariant.core.Value.Int32;
+import eu.mulk.jgvariant.core.Value.Int64;
+import eu.mulk.jgvariant.core.Value.Int8;
+import eu.mulk.jgvariant.core.Value.Maybe;
+import eu.mulk.jgvariant.core.Value.Str;
+import eu.mulk.jgvariant.core.Value.Structure;
+import eu.mulk.jgvariant.core.Value.Variant;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.RecordComponent;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Optional;
+import org.jetbrains.annotations.Nullable;
+
+/**
+ * Type class for decodable {@link Value} types.
+ *
+ * <p>Use the {@code of*} family of constructor methods to acquire a suitable {@link Decoder} for
+ * the type you wish to decode.
+ *
+ * @param <T> the type that the {@link Decoder} can decode.
+ */
+@SuppressWarnings("java:S1610")
+public abstract class Decoder<T extends Value> {
+
+  private Decoder() {}
+
+  /**
+   * @throws java.nio.BufferUnderflowException if the byte buffer is shorter than the requested
+   *     data.
+   */
+  public abstract T decode(ByteBuffer byteSlice);
+
+  abstract byte alignment();
+
+  @Nullable
+  abstract Integer fixedSize();
+
+  final boolean hasFixedSize() {
+    return fixedSize() != null;
+  }
+
+  public Decoder<T> withByteOrder(ByteOrder byteOrder) {
+    var delegate = this;
+
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return delegate.alignment();
+      }
+
+      @Override
+      public @Nullable Integer fixedSize() {
+        return delegate.fixedSize();
+      }
+
+      @Override
+      public T decode(ByteBuffer byteSlice) {
+        byteSlice.order(byteOrder);
+        return delegate.decode(byteSlice);
+      }
+    };
+  }
+
+  public static <U extends Value> Decoder<Array<U>> ofArray(Decoder<U> elementDecoder) {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return elementDecoder.alignment();
+      }
+
+      @Override
+      @Nullable
+      Integer fixedSize() {
+        return null;
+      }
+
+      @Override
+      public Array<U> decode(ByteBuffer byteSlice) {
+        List<U> elements;
+
+        var elementSize = elementDecoder.fixedSize();
+        if (elementSize != null) {
+          // A simple C-style array.
+          elements = new ArrayList<>(byteSlice.limit() / elementSize);
+          for (int i = 0; i < byteSlice.limit(); i += elementSize) {
+            var element = elementDecoder.decode(byteSlice.slice(i, elementSize));
+            elements.add(element);
+          }
+        } else {
+          // An array with aligned elements and a vector of framing offsets in the end.
+          int framingOffsetSize = byteCount(byteSlice.limit());
+          int lastFramingOffset =
+              getIntN(byteSlice.slice(byteSlice.limit() - framingOffsetSize, framingOffsetSize));
+          int elementCount = (byteSlice.limit() - lastFramingOffset) / framingOffsetSize;
+
+          elements = new ArrayList<>(elementCount);
+          int position = 0;
+          for (int i = 0; i < elementCount; i++) {
+            int framingOffset =
+                getIntN(
+                    byteSlice.slice(lastFramingOffset + i * framingOffsetSize, framingOffsetSize));
+            elements.add(
+                elementDecoder.decode(byteSlice.slice(position, framingOffset - position)));
+            position = align(framingOffset, alignment());
+          }
+        }
+
+        return new Array<>(elements);
+      }
+    };
+  }
+
+  private static int align(int offset, byte alignment) {
+    return offset % alignment == 0 ? offset : offset + alignment - (offset % alignment);
+  }
+
+  private static int getIntN(ByteBuffer byteSlice) {
+    var intBytes = new byte[4];
+    byteSlice.get(intBytes, 0, Math.min(4, byteSlice.limit()));
+    return ByteBuffer.wrap(intBytes).order(LITTLE_ENDIAN).getInt();
+  }
+
+  @SuppressWarnings("java:S3358")
+  private static int byteCount(int n) {
+    return n < (1 << 8) ? 1 : n < (1 << 16) ? 2 : 4;
+  }
+
+  public static <U extends Value> Decoder<Maybe<U>> ofMaybe(Decoder<U> elementDecoder) {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return elementDecoder.alignment();
+      }
+
+      @Override
+      @Nullable
+      Integer fixedSize() {
+        return null;
+      }
+
+      @Override
+      public Maybe<U> decode(ByteBuffer byteSlice) {
+        if (!byteSlice.hasRemaining()) {
+          return new Maybe<>(Optional.empty());
+        } else {
+          if (!elementDecoder.hasFixedSize()) {
+            // Remove trailing zero byte.
+            byteSlice.limit(byteSlice.limit() - 1);
+          }
+
+          return new Maybe<>(Optional.of(elementDecoder.decode(byteSlice)));
+        }
+      }
+    };
+  }
+
+  @SafeVarargs
+  public static <U extends Record> Decoder<Structure<U>> ofStructure(
+      Class<U> recordType, Decoder<? extends Value>... componentDecoders) {
+    var recordComponents = recordType.getRecordComponents();
+    if (componentDecoders.length != recordComponents.length) {
+      throw new IllegalArgumentException(
+          "number of decoders (%d) does not match number of structure components (%d)"
+              .formatted(componentDecoders.length, recordComponents.length));
+    }
+
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return (byte) Arrays.stream(componentDecoders).mapToInt(Decoder::alignment).max().orElse(1);
+      }
+
+      @Override
+      public Integer fixedSize() {
+        int position = 0;
+        for (var componentDecoder : componentDecoders) {
+          var fixedComponentSize = componentDecoder.fixedSize();
+          if (fixedComponentSize == null) {
+            return null;
+          }
+
+          position = align(position, componentDecoder.alignment());
+          position += fixedComponentSize;
+        }
+
+        if (position == 0) {
+          return 1;
+        }
+
+        return align(position, alignment());
+      }
+
+      @Override
+      public Structure<U> decode(ByteBuffer byteSlice) {
+        int framingOffsetSize = byteCount(byteSlice.limit());
+
+        var recordConstructorArguments = new Object[recordComponents.length];
+
+        int position = 0;
+        int framingOffsetIndex = 0;
+        int componentIndex = 0;
+        for (var componentDecoder : componentDecoders) {
+          position = align(position, componentDecoder.alignment());
+
+          var fixedComponentSize = componentDecoder.fixedSize();
+          if (fixedComponentSize != null) {
+            recordConstructorArguments[componentIndex] =
+                componentDecoder.decode(byteSlice.slice(position, fixedComponentSize));
+            position += fixedComponentSize;
+          } else {
+            if (componentIndex == recordComponents.length - 1) {
+              // The last component never has a framing offset.
+              int endPosition = byteSlice.limit() - framingOffsetIndex * framingOffsetSize;
+              recordConstructorArguments[componentIndex] =
+                  componentDecoder.decode(byteSlice.slice(position, endPosition - position));
+              position = endPosition;
+            } else {
+              int framingOffset =
+                  getIntN(
+                      byteSlice.slice(
+                          byteSlice.limit() - (1 + framingOffsetIndex) * framingOffsetSize,
+                          framingOffsetSize));
+              recordConstructorArguments[componentIndex] =
+                  componentDecoder.decode(byteSlice.slice(position, framingOffset - position));
+              position = framingOffset;
+              ++framingOffsetIndex;
+            }
+          }
+
+          ++componentIndex;
+        }
+
+        try {
+          var recordComponentTypes =
+              Arrays.stream(recordType.getRecordComponents())
+                  .map(RecordComponent::getType)
+                  .toArray(Class<?>[]::new);
+          var recordConstructor = recordType.getDeclaredConstructor(recordComponentTypes);
+          return new Structure<>(recordConstructor.newInstance(recordConstructorArguments));
+        } catch (NoSuchMethodException
+            | InstantiationException
+            | IllegalAccessException
+            | InvocationTargetException e) {
+          throw new IllegalStateException(e);
+        }
+      }
+    };
+  }
+
+  public static Decoder<Variant> ofVariant() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 8;
+      }
+
+      @Override
+      @Nullable
+      Integer fixedSize() {
+        return null;
+      }
+
+      @Override
+      public Variant decode(ByteBuffer byteSlice) {
+        // TODO
+        throw new UnsupportedOperationException("not implemented");
+      }
+    };
+  }
+
+  public static Decoder<Bool> ofBoolean() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 1;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 1;
+      }
+
+      @Override
+      public Bool decode(ByteBuffer byteSlice) {
+        return new Bool(byteSlice.get() != 0);
+      }
+    };
+  }
+
+  public static Decoder<Int8> ofInt8() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 1;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 1;
+      }
+
+      @Override
+      public Int8 decode(ByteBuffer byteSlice) {
+        return new Int8(byteSlice.get());
+      }
+    };
+  }
+
+  public static Decoder<Int16> ofInt16() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 2;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 2;
+      }
+
+      @Override
+      public Int16 decode(ByteBuffer byteSlice) {
+        return new Int16(byteSlice.getShort());
+      }
+    };
+  }
+
+  public static Decoder<Int32> ofInt32() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 4;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 4;
+      }
+
+      @Override
+      public Int32 decode(ByteBuffer byteSlice) {
+        return new Int32(byteSlice.getInt());
+      }
+    };
+  }
+
+  public static Decoder<Int64> ofInt64() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 8;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 8;
+      }
+
+      @Override
+      public Int64 decode(ByteBuffer byteSlice) {
+        return new Int64(byteSlice.getLong());
+      }
+    };
+  }
+
+  public static Decoder<Float64> ofFloat64() {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 8;
+      }
+
+      @Override
+      public Integer fixedSize() {
+        return 8;
+      }
+
+      @Override
+      public Float64 decode(ByteBuffer byteSlice) {
+        return new Float64(byteSlice.getDouble());
+      }
+    };
+  }
+
+  public static Decoder<Str> ofStr(Charset charset) {
+    return new Decoder<>() {
+      @Override
+      public byte alignment() {
+        return 1;
+      }
+
+      @Override
+      @Nullable
+      Integer fixedSize() {
+        return null;
+      }
+
+      @Override
+      public Str decode(ByteBuffer byteSlice) {
+        byteSlice.limit(byteSlice.limit() - 1);
+        return new Str(charset.decode(byteSlice).toString());
+      }
+    };
+  }
+}
diff --git a/src/main/java/eu/mulk/jgvariant/core/Value.java b/src/main/java/eu/mulk/jgvariant/core/Value.java
new file mode 100644
index 0000000..969f240
--- /dev/null
+++ b/src/main/java/eu/mulk/jgvariant/core/Value.java
@@ -0,0 +1,35 @@
+package eu.mulk.jgvariant.core;
+
+import java.util.List;
+import java.util.Optional;
+
+/** A value representable by the GVariant serialization format. */
+public sealed interface Value {
+
+  // Composite types
+  record Array<T extends Value>(List<T> values) implements Value {}
+
+  record Maybe<T extends Value>(Optional<T> value) implements Value {}
+
+  record Structure<T extends Record>(T values) implements Value {}
+
+  record Variant(Class<? extends Value> type, Value value) implements Value {}
+
+  // Primitive types
+  record Bool(boolean value) implements Value {
+    static Bool TRUE = new Bool(true);
+    static Bool FALSE = new Bool(false);
+  }
+
+  record Int8(byte value) implements Value {}
+
+  record Int16(short value) implements Value {}
+
+  record Int32(int value) implements Value {}
+
+  record Int64(long value) implements Value {}
+
+  record Float64(double value) implements Value {}
+
+  record Str(String value) implements Value {}
+}
diff --git a/src/main/java/module-info.java b/src/main/java/module-info.java
new file mode 100644
index 0000000..8880c0b
--- /dev/null
+++ b/src/main/java/module-info.java
@@ -0,0 +1,7 @@
+module eu.mulk.jgvariant.core {
+  requires java.base;
+  requires com.google.errorprone.annotations;
+  requires org.jetbrains.annotations;
+
+  exports eu.mulk.jgvariant.core;
+}
diff --git a/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java b/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
new file mode 100644
index 0000000..4deb8bc
--- /dev/null
+++ b/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
@@ -0,0 +1,278 @@
+package eu.mulk.jgvariant.core;
+
+import static java.nio.ByteOrder.LITTLE_ENDIAN;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import eu.mulk.jgvariant.core.Value.Array;
+import eu.mulk.jgvariant.core.Value.Bool;
+import eu.mulk.jgvariant.core.Value.Int32;
+import eu.mulk.jgvariant.core.Value.Int8;
+import eu.mulk.jgvariant.core.Value.Maybe;
+import eu.mulk.jgvariant.core.Value.Str;
+import eu.mulk.jgvariant.core.Value.Structure;
+import java.nio.ByteBuffer;
+import java.util.List;
+import java.util.Optional;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests based on the examples given in <a
+ * href="https://people.gnome.org/~desrt/gvariant-serialisation.pdf">~desrt/gvariant-serialisation.pdf</a>.
+ */
+class DecoderTest {
+
+  @Test
+  void testString() {
+    var data = new byte[] {0x68, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x77, 0x6F, 0x72, 0x6C, 0x64, 0x00};
+    var decoder = Decoder.ofStr(UTF_8);
+    assertEquals(new Str("hello world"), decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testMaybe() {
+    var data =
+        new byte[] {0x68, 0x65, 0x6C, 0x6C, 0x6F, 0x20, 0x77, 0x6F, 0x72, 0x6C, 0x64, 0x00, 0x00};
+    var decoder = Decoder.ofMaybe(Decoder.ofStr(UTF_8));
+    assertEquals(
+        new Maybe<>(Optional.of(new Str("hello world"))), decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testBooleanArray() {
+    var data = new byte[] {0x01, 0x00, 0x00, 0x01, 0x01};
+    var decoder = Decoder.ofArray(Decoder.ofBoolean());
+    assertEquals(
+        new Array<>(List.of(Bool.TRUE, Bool.FALSE, Bool.FALSE, Bool.TRUE, Bool.TRUE)),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testStructure() {
+    var data =
+        new byte[] {
+          0x66, 0x6F, 0x6F, 0x00, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, (byte) 0xFF, 0x04
+        };
+
+    record TestRecord(Str s, Int32 i) {}
+
+    var decoder = Decoder.ofStructure(TestRecord.class, Decoder.ofStr(UTF_8), Decoder.ofInt32());
+    assertEquals(
+        new Structure<>(new TestRecord(new Str("foo"), new Int32(-1))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testComplexStructureArray() {
+    var data =
+        new byte[] {
+          0x68,
+          0x69,
+          0x00,
+          0x00,
+          (byte) 0xfe,
+          (byte) 0xff,
+          (byte) 0xff,
+          (byte) 0xff,
+          0x03,
+          0x00,
+          0x00,
+          0x00,
+          0x62,
+          0x79,
+          0x65,
+          0x00,
+          (byte) 0xff,
+          (byte) 0xff,
+          (byte) 0xff,
+          (byte) 0xff,
+          0x04,
+          0x09,
+          0x15
+        };
+
+    record TestRecord(Str s, Int32 i) {}
+
+    var decoder =
+        Decoder.ofArray(
+            Decoder.ofStructure(
+                TestRecord.class,
+                Decoder.ofStr(UTF_8),
+                Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN)));
+    assertEquals(
+        new Array<>(
+            List.of(
+                new Structure<>(new TestRecord(new Str("hi"), new Int32(-2))),
+                new Structure<>(new TestRecord(new Str("bye"), new Int32(-1))))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testStringArray() {
+    var data =
+        new byte[] {
+          0x69, 0x00, 0x63, 0x61, 0x6E, 0x00, 0x68, 0x61, 0x73, 0x00, 0x73, 0x74, 0x72, 0x69, 0x6E,
+          0x67, 0x73, 0x3F, 0x00, 0x02, 0x06, 0x0a, 0x13
+        };
+    var decoder = Decoder.ofArray(Decoder.ofStr(UTF_8));
+    assertEquals(
+        new Array<>(List.of(new Str("i"), new Str("can"), new Str("has"), new Str("strings?"))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testNestedStructure() {
+    var data =
+        new byte[] {
+          0x69, 0x63, 0x61, 0x6E, 0x00, 0x68, 0x61, 0x73, 0x00, 0x73, 0x74, 0x72, 0x69, 0x6E, 0x67,
+          0x73, 0x3F, 0x00, 0x04, 0x0d, 0x05
+        };
+
+    record TestChild(Int8 b, Str s) {}
+    record TestParent(Structure<TestChild> tc, Array<Str> as) {}
+
+    var decoder =
+        Decoder.ofStructure(
+            TestParent.class,
+            Decoder.ofStructure(TestChild.class, Decoder.ofInt8(), Decoder.ofStr(UTF_8)),
+            Decoder.ofArray(Decoder.ofStr(UTF_8)));
+
+    assertEquals(
+        new Structure<>(
+            new TestParent(
+                new Structure<>(new TestChild(new Int8((byte) 0x69), new Str("can"))),
+                new Array<>(List.of(new Str("has"), new Str("strings?"))))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testSimpleStructure() {
+    var data = new byte[] {0x60, 0x70};
+
+    record TestRecord(Int8 b1, Int8 b2) {}
+
+    var decoder =
+        Decoder.ofStructure(
+            TestRecord.class,
+            Decoder.ofInt8().withByteOrder(LITTLE_ENDIAN),
+            Decoder.ofInt8().withByteOrder(LITTLE_ENDIAN));
+
+    assertEquals(
+        new Structure<>(new TestRecord(new Int8((byte) 0x60), new Int8((byte) 0x70))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testPaddedStructureRight() {
+    var data = new byte[] {0x60, 0x00, 0x00, 0x00, 0x70, 0x00, 0x00, 0x00};
+
+    record TestRecord(Int32 b1, Int8 b2) {}
+
+    var decoder =
+        Decoder.ofStructure(
+            TestRecord.class,
+            Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN),
+            Decoder.ofInt8().withByteOrder(LITTLE_ENDIAN));
+
+    assertEquals(
+        new Structure<>(new TestRecord(new Int32(0x60), new Int8((byte) 0x70))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testPaddedStructureLeft() {
+    var data = new byte[] {0x60, 0x00, 0x00, 0x00, 0x70, 0x00, 0x00, 0x00};
+
+    record TestRecord(Int8 b1, Int32 b2) {}
+
+    var decoder =
+        Decoder.ofStructure(
+            TestRecord.class,
+            Decoder.ofInt8().withByteOrder(LITTLE_ENDIAN),
+            Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN));
+
+    assertEquals(
+        new Structure<>(new TestRecord(new Int8((byte) 0x60), new Int32(0x70))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testSimpleStructureArray() {
+    var data =
+        new byte[] {
+          0x60,
+          0x00,
+          0x00,
+          0x00,
+          0x70,
+          0x00,
+          0x00,
+          0x00,
+          (byte) 0x88,
+          0x02,
+          0x00,
+          0x00,
+          (byte) 0xF7,
+          0x00,
+          0x00,
+          0x00
+        };
+
+    record TestRecord(Int32 b1, Int8 b2) {}
+
+    var decoder =
+        Decoder.ofArray(
+            Decoder.ofStructure(
+                TestRecord.class,
+                Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN),
+                Decoder.ofInt8().withByteOrder(LITTLE_ENDIAN)));
+
+    assertEquals(
+        new Array<>(
+            List.of(
+                new Structure<>(new TestRecord(new Int32(96), new Int8((byte) 0x70))),
+                new Structure<>(new TestRecord(new Int32(648), new Int8((byte) 0xf7))))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testByteArray() {
+    var data = new byte[] {0x04, 0x05, 0x06, 0x07};
+
+    var decoder = Decoder.ofArray(Decoder.ofInt8());
+
+    assertEquals(
+        new Array<>(
+            List.of(
+                new Int8((byte) 0x04),
+                new Int8((byte) 0x05),
+                new Int8((byte) 0x06),
+                new Int8((byte) 0x07))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testIntegerArray() {
+    var data = new byte[] {0x04, 0x00, 0x00, 0x00, 0x02, 0x01, 0x00, 0x00};
+
+    var decoder = Decoder.ofArray(Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN));
+
+    assertEquals(
+        new Array<>(List.of(new Int32(4), new Int32(258))), decoder.decode(ByteBuffer.wrap(data)));
+  }
+
+  @Test
+  void testDictionaryEntry() {
+    var data =
+        new byte[] {0x61, 0x20, 0x6B, 0x65, 0x79, 0x00, 0x00, 0x00, 0x02, 0x02, 0x00, 0x00, 0x06};
+
+    record TestEntry(Str key, Int32 value) {}
+
+    var decoder =
+        Decoder.ofStructure(
+            TestEntry.class, Decoder.ofStr(UTF_8), Decoder.ofInt32().withByteOrder(LITTLE_ENDIAN));
+    assertEquals(
+        new Structure<>(new TestEntry(new Str("a key"), new Int32(514))),
+        decoder.decode(ByteBuffer.wrap(data)));
+  }
+}